1. Field of the Invention
This invention relates to novel methods, devices and apparatuses for the centrifugal separation of a liquid into its components of varying specific gravities, and is more particularly directed toward a blood separation device useful, for example, in the separation of blood components for use in various therapeutic regimens.
2. Description of the State of Art
Centrifugation utilizes the principle that particles suspended in solution will assume a particular radial position within the centrifuge rotor based upon their respective densities and will therefore separate when the centrifuge is rotated at an appropriate angular velocity for an appropriate period of time. Centrifigal liquid processing systems have found applications in a wide variety of fields. For example, centrifugation is widely used in blood separation techniques to separate blood into its component parts, that is, red blood cells, platelets, white blood cells, and plasma.
The liquid portion of the blood, referred to as plasma, is a protein-salt solution in which red and white blood cells and platelets are suspended. Plasma, which is 90 percent water, constitutes about 55 percent of the total blood volume. Plasma contains albumin (the chief protein constituent), fibrinogen (responsible, in part, for the clotting of blood), globulins (including antibodies) and other clotting proteins. Plasma serves a variety of functions, from maintaining a satisfactory blood pressure and providing volume to supplying critical proteins for blood clotting and immunity. Plasma is obtained by separating the liquid portion of blood from the cells suspended therein.
Red blood cells (erythrocytes) are perhaps the most recognizable component of whole blood. Red blood cells contain hemoglobin, a complex iron-containing protein that carries oxygen throughout the body while giving blood its red color. The percentage of blood volume composed of red blood cells is called the xe2x80x9chematocrit.xe2x80x9d
White blood cells (leukocytes) are responsible for protecting the body from invasion by foreign substances such as bacteria, fungi and viruses. Several types of white blood cells exist for this purpose, such as granulocytes and macrophages which protect against infection by surrounding and destroying invading bacteria and viruses, and lymphocytes which aid in the immune defense.
Platelets (thrombocytes) are very small cellular components of blood that help the clotting process by sticking to the lining of blood vessels. Platelets are vital to life, because they help prevent both massive blood loss resulting from trauma and blood vessel leakage that would otherwise occur in the course of normal, day-to-day activity.
If whole blood is collected and prevented from clotting by the addition of an appropriate anticoagulant, it can be centrifuged into its component parts. Centrifugation will result in the red blood cells, which weigh the most, packing to the most outer portion of the rotating container, while plasma, being the least dense will settle in the central portion of the rotating container. Separating the plasma and red blood cells is a thin white or grayish layer called the buffy coat. The buffy coat layer consists of the white blood cells and platelets, which together make up about 1 percent of the total blood volume.
These blood components, discussed above, may be isolated and utilized in a wide range of diagnostic and therapeutic regimens. For example, red blood cells are routinely transfused into patients with chronic anemia resulting from disorders such as kidney failure, malignancies, or gastrointestinal bleeding and those with acute blood loss resulting from trauma or surgery. The plasma component is typically frozen by cryoprecipitation and then slowly thawed to produce cryoprecipitated antihemophiliac factor (AHF) which is rich in certain clotting factors, including Factor VIII, fibrinogen, von Willebrand factor and Factor XIII. Cryoprecipitated AHF is used to prevent or control bleeding in individuals with hemophilia and von Willebrand""s disease. Platelets and white blood cells, which are found in the buffy layer component, can be used to treat patients with abnormal platelet function (thrombocytopenia) and patients that are unresponsive to antibiotic therapy, respectively.
Various techniques and apparatus have been developed to facilitate the collection of whole blood and the subsequent separation of therapeutic components therefrom. Centrifugal systems, also referred to as blood-processing systems, generally fall into two categories, discontinuous-flow and continuous-flow devices.
In discontinuous-flow systems, whole blood from the donor or patient flows through a conduit into the rotor or bowl where component separation takes place. These systems employ a bowl-type rotor with a relatively large (typically 200 ml or more) volume that must be filled with blood before any of the desired components can be harvested. When the bowl is full, the drawing of fresh blood is stopped, the whole blood is separated into its components by centrifugation, and the unwanted components are returned to the donor or patient through the same conduit intermittently, in batches, rather than on a continuous basis. When the return has been completed, whole blood is again drawn from the donor or patient, and a second cycle begins. This process continues until the required amount of the desired component has been collected. Discontinuous-flow systems have the advantage that the rotors are relatively small in diameter but may have the disadvantage of a relatively large extracorporeal volume (i.e., the amount of blood that is out of the donor at any given time during the process). Discontinuous-flow devices are used for the collection of platelets and/or plasma, and for the concentration and washing of red blood cells. They are used to reconstitute previously frozen red blood cells and to salvage red blood cells lost intraoperatively. Because the bowls in these systems are rigid and have a fixed volume, however, it has been difficult to control the hematocrit of the final product, particularly if the amount of blood salvaged is insufficient to fill the bowl with red blood cells.
One example of a discontinuous-flow system is disclosed by McMannis, et al., in his U.S. Pat. No. 5,316,540, and is a variable volume centrifuge for separating components of a fluid medium, comprising a centrifuge that is divided into upper and lower chambers by a flexible membrane, and a flexible processing container bag positioned in the upper chamber of the centrifuge. The McMannis, et al., system varies the volume of the upper chamber by pumping a hydraulic fluid into the lower chamber, which in turn raises the membrane and squeezes the desired component out of the centrifuge. The McMannis, et al., system takes up a fairly large amount of space, and its flexible pancake-shaped rotor is awkward to handle. The McMannis, et al., system does not permit the fluid medium to flow into and out of the processing bag at the same time, nor does it permit fluid medium to be pulled out of the processing bag by suction.
In continuous-flow systems, whole blood from the donor or patient also flows through one conduit into the spinning rotor where the components are separated. The component of interest is collected and the unwanted components are returned to the donor through a second conduit on a continuous basis as more whole blood is being drawn. Because the rate of drawing and the rate of return are substantially the same, the extracorporeal volume, or the amount of blood that is out of the donor or patient at any given time in the procedure, is relatively small. These systems typically employ a belt-type rotor, which has a relatively large diameter but a relatively small (typically 100 ml or less) processing volume. Although continuous-flow systems have the advantage that the amount of blood that must be outside the donor or patient can be relatively small, they have the disadvantage that the diameter of the rotor is large. These systems are, as a consequence, large. Furthermore, they are complicated to set up and use. These devices are used almost exclusively for the collection of platelets.
Continuous-flow systems are comprised of rotatable and stationary parts that are in fluid communication. Consequently, continuous-flow systems utilize either rotary seals or a J-loop. A variety of types of rotary centrifuge seals have been developed. Some examples of rotary centrifuge seals which have proven to be successful are described in U.S. Pat. Nos. 3,409,203 and 3,565,330, issued to Latham. In these patents, rotary seals are disclosed which are formed from a stationary rigid low friction member in contact with a moving rigid member to create a dynamic seal, and an elastomeric member which provides a resilient static seal as well as a modest closing force between the surfaces of the dynamic seal.
Another rotary seal suitable for use in blood-processing centrifuges is described in U.S. Pat. No. 3,801,142 issued to Jones, et al. In this rotary seal, a pair of seal elements having confronting annular fluid-tight sealing surfaces of non-corrodible material are provided. These are maintained in a rotatable but fluid-tight relationship by axial compression of a length of elastic tubing forming one of the fluid connections to these seal elements.
Related types of systems which incorporate rotatable, disposable annular separation chambers coupled via rotary seals to stationary tubing members are disclosed in U.S. Pat. Nos. 4,387,848; 4,094,461; 4,007,871; and 4,010,894.
One drawback present in the above-described continuous-flow systems has been their use of a rotating seal or coupling element between that portion of the system carried by the centrifuge rotor and that portion of the system which remains stationary. While such rotating seals have provided generally satisfactory performance, they have been expensive to manufacture and have unnecessarily added to the cost of the flow systems. Furthermore, such rotating seals introduce an additional component into the system which if defective can cause contamination of the blood being processed.
One flow system heretofore contemplated to overcome the problem of the rotating seal utilizes a rotating carriage on which a single housing is rotatably mounted. An umbilical cable extending to the housing from a stationary point imparts planetary motion to the housing and thus prevents the cable from twisting. To promote sterile processing while avoiding the disadvantages of a discontinuous-flow system within a single sealed system, a family of dual member centrifuges can be used to effect cell separation. One example of this type of centrifuge is disclosed in U.S. Pat. No. RE 29,738 to Adams entitled xe2x80x9cApparatus for Providing Energy Communication Between a Moving and a Stationary Terminal.xe2x80x9d Due to the characteristics of such dual member centrifuges, it is possible to rotate a container containing a fluid, such as a unit of donated blood and to withdraw a separated fluid component, such as plasma, into a stationary container, outside of the centrifuge without using rotating seals. Such container systems utilize a J-loop and can be formed as closed, sterile transfer sets.
The Adams patent discloses a centrifuge having an outer rotatable member and an inner rotatable member. The inner member is positioned within and rotatably supported by the outer member. The outer member rotates at one rotational velocity, usually called xe2x80x9cone omega,xe2x80x9d and the inner rotatable member rotates at twice the rotational velocity of the outer housing or xe2x80x9ctwo omega.xe2x80x9d There is thus a one omega difference in rotational speed of the two members. For purposes of this document, the term xe2x80x9cdual member centrifugexe2x80x9d shall refer to centrifuges of the Adams type.
The dual member centrifuge of the Adams patent is particularly advantageous in that, as noted above, no seals are needed between the container of fluid being rotated and the non-moving component collection containers. The system of the Adams patent provides a way to process blood into components in a single, sealed, sterile system wherein whole blood from a donor can be infused into the centrifuge while the two members of the centrifuge are being rotated.
An alternate to the apparatus of the Adams patent is illustrated in U.S. Pat. No. 4,056,224 to Lolachi entitled xe2x80x9cFlow System for Centrifugal Liquid Processing Apparatus.xe2x80x9d The system of the Lolachi patent includes a dual member centrifuge of the Adams type. The outer member of the Lolachi centrifuge is rotated by a single electric motor which is coupled to the internal rotatable housing by belts and shafts.
U.S. Pat. No. 4,108,353 to Brown entitled xe2x80x9cCentrifugal Apparatus With Oppositely Positioned Rotational Support Meansxe2x80x9d discloses a centrifuge structure of the Adams type which includes two separate electrical motors. One electric motor is coupled by a belt to the outer member and rotates the outer member at a desired nominal rotational velocity. The second motor is carried within the rotating exterior member and rotates the inner member at the desired higher velocity, twice that of the exterior member.
U.S. Pat. No. 4,109,855 to Brown, et al., entitled xe2x80x9cDrive System For Centrifugal Processing Apparatusxe2x80x9d discloses yet another drive system. The system of the Brown, et al., patent has an outer shaft, affixed to the outer member for rotating the outer member at a selected velocity. An inner shaft, coaxial with the outer shaft, is coupled to the inner member. The inner shaft rotates the inner member at twice the rotational velocity as the outer member. A similar system is disclosed in U.S. Pat. No. 4,109,854 to Brown entitled xe2x80x9cCentrifugal Apparatus With Outer Enclosure.xe2x80x9d
The continuous-flow systems described above are large and expensive units that are not intended to be portable. Further, they are also an order of magnitude more expensive than a standard, multi-container blood collection set. There exists the need, therefore, for a centrifugal system for processing blood and other biological fluids that is compact and easy to use and that addresses the disadvantages of prior-art discontinuous and continuous-flow systems.
Whole blood that is to be separated into its components is commonly collected into a flexible plastic donor bag, and the blood is centrifuged to separate it into its components through a batch process. This is done by spinning the blood bag for a period of about 10 minutes in a large refrigerated centrifuge. The main blood constituents, i.e., red blood cells, platelets and white cells, and plasma, having sedimented and formed distinct layers, are then expressed sequentially by a manual extractor in multiple satellite bags attached to the primary bag.
More recently, automated extractors have been introduced in order to facilitate the manipulation. Nevertheless, the whole process remains laborious and requires the separation to occur within a certain time frame to guarantee the quality of the blood components. This complicates the logistics, especially considering that most blood donations are performed in decentralized locations where no batch processing capabilities exist.
This method has been practiced since the widespread use of the disposable plastic bags for collecting blood in the 1970""s and has not evolved significantly since then. Some attempts have been made to apply haemapheresis technology in whole blood donation. This technique consists of drawing and extracting on-line one or more blood components while a donation is performed, and returning the remaining constituents to the donor. However, the complexity and costs of haemapheresis systems preclude their use by transfusion centers for routine whole blood collection.
There have been various proposals for portable, disposable, centrifugal apparatus, usually with collapsible bags, for example as in U.S. Pat. Nos. 3,737,096, or 4,303,193 to Latham, Jr., or with a rigid walled bowl as in U.S. Pat. No. 4,889,524 to Fell, et al. These devices all have a minimum fixed holding volume which requires a minimum volume usually of about 250 ml to be processed before any components can be collected.
U.S. Pat. No. 5,316,540 to McMannis, et al., discloses a centrifugal processing apparatus, wherein the processing chamber is a flexible processing bag which can be deformed to fill it with biological fluid or empty it by means of a membrane which forms part of the drive unit. The bag comprises a single inlet/outlet tubing for the introduction and removal of fluids to the bag, and consequently cannot be used in a continual, on-line process. Moreover, the processing bag has a the disadvantage of having 650 milliliter capacity, which makes the McMannis, et al., device difficult to use as a blood processing device.
As discussed above, centrifuges are often used to separate blood into its components for use in a variety of therapeutic regimens. One such application is the preparation of a bioadhesive sealant. A bioadhesive sealant, also referred to as fibrin glue, is a relatively new technological advance which attempts to duplicate the biological process of the final stage of blood coagulation. Clinical reports document the utility of fibrin glue in a variety of surgical fields, such as, cardiovascular, thoracic, transplantation, head and neck, oral, gastrointestinal, orthopedic, neurosurgical, and plastic surgery. At the time of surgery, the two primary components comprising the fibrin glue, fibrinogen and thrombin, are mixed together to form a clot. The clot is applied to the appropriate site, where it adheres to the necessary tissues, bone, or nerve within seconds, but is then slowly reabsorbed by the body in approximately 10 days by fibrinolysis. Important features of fibrin glue is its ability to: (1) achieve haemostasis at vascular anastomoses particularly in areas which are difficult to approach with sutures or where suture placement presents excessive risk; (2) control bleeding from needle holes or arterial tears which cannot be controlled by suturing alone; and (3) obtain haemostasis in heparinized patients or those with coagulopathy. See, Borst, H. G., et al., J Thorac. Cardiovasc. Surg., 84:548-553 (1982); Walterbusch, G. J, et al., Thorac. Cardiovasc. Surg., 30:234-23 5 (1982); and Wolner, F. J, et al., Thorac. Cardiovasc. Surg., 30:236-237 (1982).
There is still a need, therefore, for a centrifugal system for processing blood and other biological fluids, that is compact and easy to use and that does not have the disadvantages of prior-art discontinuous and/or continuous flow systems and furthermore there exists a need for a convenient and practical method for preparing a platelet gel composition wherein the resulting platelet gel poses a zero risk of disease transmission and a zero risk of causing an adverse physiological reaction.
There is also a widespread need for a system that, during blood collection, will automatically separate the different components of whole blood that are differentiable in density and size, with a simple, low cost, disposable unit.
There is further a need for a centrifugal cell processing system wherein multiple batches of cells can be simultaneously and efficiently processed without the use of rotational coupling elements.
Preferably the apparatus will be essentially self-contained. Preferably, the equipment needed to practice the method will be relatively inexpensive and the blood contacting set will be disposable each time the whole blood has been separated.
Accordingly, an object of this invention is to provide a method and apparatus for the separation of components suspended or dissolved in a fluid medium by centrifugation. More specifically, one object of this invention is to provide a method for the separation and isolation of one or more whole blood components, such as platelet rich plasma, white blood cells and platelet poor plasma, from anticoagulated whole blood by centrifugation, wherein the components are isolated while the centrifuge is rotating.
To achieve the foregoing, an embodiment of the present invention provides a centrifuge disposable or separation assembly having at least one collection chamber for receiving and holding a fluid medium to be centrifuged, the chamber having an outer perimeter, an inner perimeter, a generally circular cross-sectional area, and a generally conical outboard or outer-perimeter collecting portion. The collection chamber is typically formed from relatively rigid, molded plastic or other materials. A mounting assembly (e.g., a caddy for the disposable) is included as part of the invention to allow accurate mounting of the centrifuge disposable relative to the centrifuge rotor to facilitate balanced distribution of component weights for smooth centrifuge rotation and to allow quick installation and release of the centrifuge disposal after use for easy insertion and replacement without tools.
The collection chamber further includes a first and second port in fluid communication with opposite points near the outer most or outboard portions of the chamber (e.g., in the conical collecting portion). The first and second ports thus provide fluid communication with the environment inside and outside of the collection chamber. The first and second ports are in turn fluidly connected to a lumen tubing, which may be single lumen for discontinuous-flow embodiments in which a single tube is used for fill and extraction and multi-lumen for continuous fill and extraction embodiments in which an inlet lumen is used for fill and one or more outlet lumens are used for extraction of separated components.
Once a desired degree of separation of whole blood has been achieved as determined by process timing and/or sensors, the present invention provides for the specific removal or extraction of the desired fraction within one or more of the regions from collection chamber of the centrifuge disposable through the outlet tube during continued rotation of the centrifuge, thereby allowing for on-line removal of the desired fraction. In continuous-flow embodiments, additional aliquots may be added to the centrifuge disposable via the inlet tube simultaneously or after the desired component has been harvested. Generally, in discontinuous-flow embodiments, the collection chamber of the centrifuge disposable is initially filled during a lower speed rotation, the collection chamber is then rotated at higher speeds to achieve a desired separation or outward packing of heavier components, the desired fluid components are then collected (often with the aid of sensors), the collection chamber is emptied, and the collection chamber is refilled to begin additional separation processes (often the collection chamber and centrifuge disposable will be replaced prior to a next processing of fluid, e.g., blood).
According to an important aspect of the invention, the separation assembly or centrifuge disposable is configured to be volume insensitive by providing ongoing or self-balancing and to be hemocrit insensitive by facilitating the accurate collection of a desired component (such as plasma) without unwanted components (such as red blood cells). To provide ongoing balancing, the separation assembly preferably has two or more collection chambers or reservoirs that are simultaneously filled or drawn down (or two or more inlet ports to a single chamber). In one embodiment, two elongated collection chambers are provided and positioned such that their central axes substantially coincide. Further, a single fill line is provided that branches to an inlet/outlet port on the outboard end of each collection chamber (although in multi-lumen tubing embodiments, the inlet lumen terminates at a point in the chamber interior to the outlet lumen) or at points about 180 degrees apart. In other embodiments, 3 or more collection chambers are provided and are equidistantly positioned to provide similar ongoing balancing (e.g., three collection chambers may be provided spaced about 120 degrees apart or four collection chambers may be provided spaced about 90 degrees apart).
To facilitate component collection or hemocrit insensitivity, each collection chamber preferably combines an elongated portion for providing a larger volume reservoir with an outboard or outer collection portion that has tapered sides that angle inward toward the central axis of the collection chamber. In one embodiment, the inner, elongated portion is cylindrical in shape with smooth walls that extend substantially parallel to the chamber central axis while the adjoining outer, collection portion is conical in shape with a taper or angle selected based on the size of the cells or components being collected. At the most outboard or outer location on the collection portion, the collection chamber includes a port or connection point for the lumen tubing. The conical shape of the outer collection portion creates tapered inner walls in the chamber that allows small percentage components (such as platelets and white blood cells) to be collected in a smaller volume portion of the chamber. This is important for sensing where two separate component volumes mate or contact because the small volume components will have a larger radial component within the collection chamber in the conical collection portion near the port than in the larger volume straight-walled inner portion. Hence, for identifying and collecting very small components in a separated fluid, a larger taper is preferred to provide a smaller collection volume in the chamber near the port. A sensor, such as a visible red LED, is typically provided in the outer collection portion adjacent the port to detect interfaces between separated components.
In one embodiment, accurate collection of fluid components is enhanced by providing a trap in the lumen tubing to control the flow of more dense components. For example, red blood cells tend to pack in the outer collection portion and then flow outward into the lumen tubing during higher speed rotation of the centrifuge. To block unwanted flow of separated components, one embodiment of the separation assembly includes a trap in the lumen tubing exterior and adjacent to the port of the collection chamber. The trap may take a number of configurations and in a preferred embodiment, the trap is a xe2x80x9cUxe2x80x9d shape in the tubing which acts to pack red blood cells or other heavier components. A trap is provided at each outer port to a collection chamber to provide this effective flow control to each collection chamber and control contamination or mixing of separated components.
Additional objects, advantages, and novel features of this invention shall be set forth in part in the description and examples that follow, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by the practice of the invention. The objects and the advantages of the invention may be realized and attained by means of the instrumentalities and in combinations particularly pointed out in the appended claims.